FR is the feedrate and will be anything between 0 and 99 depending on demand for heat. It the percentage of range specified by the MIN and MAX settings.MIN is the minimum feed setting. It is a value from 1 to 15 (default 6 for LL stoves).MAX is the maximum feed setting. It is a value from MIN up to 99 (default 40 for LL stoves).

MIN and MAX are both indications of the number of seconds of "on" time the stoker motor will be run for every 100 seconds. So, MIN of 6 means when the control is at idle (FR = 0) the stoker will be on for 6 seconds out of every 100. MAX of 40 means when maximum heat is being called for (FR = 99) the stoker will be on for 40 out of every 100 seconds.

If FR is something in between, say 37, then the stoker will be on for 37% of the on time range specified by MIN and MAX. Using default MIN and MAX, a FR of 37 would mean .37 x (40 - 6) + 6 = 18 seconds of on time per 100 seconds (we ignore fractions, we do not round up)